The sturdy harness is an item used to combine the log basket and Forestry kit into the Forestry basket, combining the functionality of both items. This process can be reversible by right clicking the Forestry basket, heading into the configure options, and then choosing the dismantle option.
Most players opt not to make the Forestry basket because players will need to unequip it in order to bank the logs. Additionally, it changes the menu options of the Forestry kit (now harness) to being predominantly basket. Moreover, players will need to go through right click options and chat box dialogue in order to view the Forestry kit, check the log basket, and also open/close the log basket.